Duality constrained meta atoms for transformation optics

TL;DR

This paper introduces a method to design dual-symmetric metamaterials for transformation optics by constraining their polarisability tensors, ensuring invariance under electromagnetic duality transformations and enabling precise control of electromagnetic fields.

Contribution

It provides explicit constraints on the polarisability tensors of meta atoms to achieve dual-symmetry in transformation optics metamaterials, linking tensor components to coordinate transformation parts.

Findings

Dual-symmetric metamaterials can implement general transformations.

Explicit expressions for polarisability tensor constraints are derived.

Electric and magnetic dipoles at the same point produce helicity-defined fields.

Abstract

Maxwell's equations in curved space-time are invariant under electromagnetic duality transformations. We exploit this property to constraint the design parameters of metamaterials used for transformations optics. We show that a general transformation must be implemented using a dual-symmetric metamaterial. This can be accomplished constraining the polarisability tensors of their individual constituents, i.e. the meta atoms. We obtain explicit expressions for these constraints. We also show that the spatial part of the coordinate transformation depends only on the electric-electric tensorial coupling of the polarisability tensor, while the spatio-temporal part depends only on the electric-magnetic tensorial coupling. In our derivations, we find that two dipoles located at the same point, one electric (p) and one magnetic (m), are needed to produce a total field with well defined helicity equal to +1 or -1, and that they must be related as p=im/c or p=-im/c, respectively.